Fe3Al介金屬利用金基填料紅外線硬銲接合之研究及新型銅基硬銲填料之開發

Abstract

本研究以兩種金基填料利用紅外線硬銲接合Fe3Al介金屬，首先利用填料對基材進行潤濕性試驗，以確定適當的加熱溫度再進行後續之接合研究。以 AuPdNi(Au-8wt.%Pd-22wt.%Ni)填料於980℃硬銲，其銲道會產生AlAu2、Fe3Al及Al2FeNi三種較硬脆的介金屬化合物，於此溫度下破壞形式皆屬於脆性破壞。而以AuCu(Au-20wt.%Cu)為填料，在不同的製程條件下進行硬銲，其破壞主要都沿著銲道中Au-Al-Cu三元合金系統中的β相作延伸，但其破壞機制與破壞形式會因不同的製程條件而有所不同，在較低溫的880℃持溫3分鐘會有最高的剪力強度327MPa，且整體呈現延性與脆性混和的破壞形式，而提高持溫時間及溫度則會使基材受到損害，且破壞形式將會轉變成脆性破壞。本研究也利用Cu-33.7%Mn合金填料對304、422與440C不銹鋼進行紅外線硬銲接合，研究結果發現，無論對何種不銹鋼進行硬銲，都會在接合的界面處發現一連續的(γFe,γMn)相，此連續相與銲道的(Cu,γMn)相間的接合性不佳而易有裂痕的產生，考慮熱膨脹係數的差異後，4系列與3系列不鏽鋼於兩相間產生裂痕的情形也有所不同。此外，上述不銹鋼於接合後，銲道中央也可發現硬銲後的凝固縮孔。於875℃持溫3分鐘硬銲304與422不銹鋼時，會沿著銲道中央的縮孔發生延性破壞，其剪力強度大約為280MPa。另外，本研究亦於Cu-33.7%Mn合金填料中添加適量的Ni元素以改善其接合性質，發現其潤濕界面顯微組織與未加Ni之Cu-33.7%Mn填料者相似；實驗中發現，隨著Ni添加得愈多，改善界面處裂痕的效果也愈明顯，當Ni為10wt.%時，在接合界面處已觀察不到任何裂紋的存在。

Microstructural evolution and bonding strength of infrared brazed Fe3Al and stainless steels(SS) using Au-based and CuMn-based fillers, respectively, are studied. Firstly the wetting experiments using these braze alloys are conducted to make sure the suitable brazing temperature. Al2FeNi, Fe3Al and AlAu2 intermetallics are found in the joint of AuPdNi (Au-8wt.%Pd-22wt.%Ni) braze alloy brazed at 980℃ and all specimens are fractured in brittle. For AuCu(Au-20wt.%Cu) braze alloy, the brazed joint is fractured along the central β-phase in which the fracture exhibits ductile/brittle mode(s) with different brazing conditions. The highest shear strength for AuCu filler is 327MPa for specimen brazed at 880℃×300s. Raising the brazing time or temperature will deteriorate the strength due to the fracture mode transfers to brittleness. For infrared brazed 304, 422 and 440C stainless steels using Cu-33.7%Mn filler, a continuous interfacial (γFe,γMn) phase is found in between the braze and SS which is not well bonded with (Cu,γMn) primary phase in the brazed joint. Thus some cracks are observed in between (γFe,γMn) and (Cu,γMn) due to the thermal expansion mismatch of these two phases. In addition, solidification shrinkage voids or impurities are also observed in the central region of the joint and the fracture mode along this central voids/impurities is ductile with the shear strength of 280MPa for brazing 304 and 422 SS brazed at 875oC×180s. Cu-33.7%Mn filler alloyed with Ni can improve the joint properties, but increase slightly the fillers’ melting points. The Ni alloyed CuMn fillers can effectively wet all SS at appropriate temperatures and the interfacial cracks in between (γFe,γMn) and (Cu,γMn) phase are greatly reduced with increasing the Ni addition.